The present invention relates to a semiconductor device and a manufacturing method thereof, and particularly to a semiconductor device and a manufacturing method thereof, in which the characteristics of the dielectric layer used in the formation of the capacitor of the memory device can be improved.
With the recent progress of the semiconductor manufacturing techniques and the expansion of its application field, the developments of large capacity memory devices are promoted. Particularly, an outstanding advancement has been achieved in improving the density of DRAM (Dynamic Random Access Memory) by developing a memory cell consisting of a single capacitor and a single transistor.
According to the memory cell structure for increasing the density of DRAM, the conventional planar type capacitor cell is evolved to a stacked type capacitor and a trenched type capacitor, and the trenched-type capacitor has been put to practical use in 1 M bit DRAM.
As the material of the dielectric layer for the capacitor of such a high density memory cell, the conventional oxide layer has been replaced with a nitride/oxide layer structure, and an oxide/nitride/oxide layer (ONO layer) which is a stacked-type, this being under diversified research. The process for manufacturing the ONO layer is illustrated in FIGS. 1A to 1D, and this will be described in brief terms below.
Firstly, an oxide layer OX1 is formed in a thickness of 10.ANG.-200.ANG. upon a capacitor substrate; a nitride layer N is formed in a thickness of 50.ANG.-200.ANG. upon the oxide layer OX1 as shown in FIG. 1B by applying a low chemical vapor deposition (to be called hereinafter "LPCVD") device; and the nitride layer N is subjected to an oxidation in a thickness of 10.ANG.-200.ANG. as shown in FIG. 1C to form a second oxide layer OX2, thereby forming a dielectric layer I fo the oxide/nitride/oxide structure.
Upon the above-described second oxide layer OX2, a polycrystalline silicon is formed in a thickness of 500.ANG.-3000.ANG. to form an upper substrate 11, thereby completing a capacitor as shown in FIG. 1D.
According to such a conventional dielectric layer manufacturing method, the nitride layer has a dielectric constant E larger by 1.9 times then the simple oxide layer, but it has disadvantages such as the crystallizing defects and pin holes produced in the layer itself and the biased impurity diffusions due to the spreading characteristics of the LPCVD device which is used in the formation of the layer. Accordingly, the leakage current is increased even under the supply voltage, thereby degrading the electrical characteristics of the capacitor.